Process for the removal of reducing sugar from polyhydric alcohol compositions



Patented Mar. 8, 1949 PROCESS FOR THE REMOVAL OF REDUCING SUGAR FROMPOLYHYDRIC ALCOHOL COMPOSITIONS John D. Brandner, Tamaqua, Pa., assignorto Atlas Powder Company, Wilmington, Del., a

corporation of Delaware No Drawing. Application September 24, 1946,Serial No. 699,077

4 Claims.

The present invention relates to the removal of reducing sugars fromcompositions comprising polyhydric alcohol and reducing sugar.

An object of the present invention is the production, from compositionscomprising polyhydric alcohol and reducing sugar, of composiziorzs whichhave a very low reducing sugar con- Another object of the invention isthe provision of a method which is particularly useful in the removal ofresidual reducing'sugar from polyhydric alcohol compositions prepared bythe reduction of reducible sugar.

Still another object of the invention is the provision of an economicalmethod of removing reducing sugars from polyhydric alcohol compositionsto produce compositions which contain the polyhydric alcohol insubstantially its original condition, that is, without substantialconversion to other products as by oxidation or internal or externaletherification.

Other objects of the invention will hereinafter more fully appear.

Polyhydric alcohol compositions frequently contain substantial amountsof reducing sugar. By reducing sugar is meant a sugar that will reduceFehlings solution at the boiling point, as for example a triose such asglyceraldehyde, a pentose such as xylose, rhamnose, and the like, ahexose such as glucose, fructose, mannose, galactose, and the like, or areducing dissacharride such as lactose, maltose, or the like.

Polyhydric alcohol compositions are often used in industrial processesunder conditions in which the presence of any substantial quantity ofreducing sugar is objectionable. Thus, for example, the polyhydricalcohol composition may be employed in chemical reactions undertemperature conditions which tend to decompose any reducing sugarpresent with resultant discoloration or other objectionable performance,either physical or chemical, or both. Consequently, the provision of amethod for the ready and economical removal of reducing sugar frompolyhydric alcohol compositions containing the same is highly desirable.

The polyhydric alcohol of the compositions from which reducing sugar isremoved in accordance with the method of the present invention may beany of the water-soluble polyhydric alcohols, such as glycol,polyglycol, glycerine, polyglycerine, erythritol, pentaerythritol,sorbitol, mannitol, dulcitol, and the like. As above indicated, themethod of the present invention is particularly applicable to thetreatment of polyhydric alcohol compositions derived from reduciblesugar and containing residual reducing sugar, as for example, sorbitolsolutions prepared by the reduction of glucose.

In the production of such polyhydric alcohol compositions by thereduction of reducible sugar it is seldom practical to carry thereduction beyond 99.9% completion. Moreover, in many such processes, therate of sugar reduction decreases very rapidly after about 90% of thesugar has been reduced. The method of the present invention issufliciently economical to make it advantageous in such processes toterminate the hydrogenation when further hydrogenation could only beaccomplished at a very low rate and to thereafter treat the polyhydricalcohol composition in accordance with the method to bring the reducingsugar down to a very low level. However, the method of the presentinvention is not to be considered as limited to the treatment ofcompositions produced by the reduction of reducible sugar as it isapplicable to polyhydric alcohols containing reducing sugar irrespectiveof the manner in which the reducing sugar became mixed with thepolyhydric alcohol.

In accordance with the method of the present invention, the polyhydricalcohol composition which contains reducing sugar is heated with a basicsubstance to effect substantial alkaline degradation of the reducingsugar and the reacted mixture is then passed through a cation exchangerand then through an anion exchanger to effect removal of the basicsubstance and of organic acid degradation products of the reducingsugar. The method is readily capable of removing over of the reducingsugar from such compositions and is particularly useful when applied tocompositions having small amounts such as 2%, or even 0.5% or less, ofreducing sugar present, to lower the reducing sugar content to less than0.1%. If desired, the method may be repeatedly applied to the polyhydricalcohol solution with resultant further lowering of the reducing sugarcontent.

Any basic substance may be employed in the alkaline degradation stepwhich is sufliciently strong to effect the alkaline degradation and beabsorbed in the cation exchanger. Preferably, a basic substance selectedfrom the group consisting of alkali and alkaline earth metal (includingmagnesium) hydroxide is employed and of these the alkali metalhydroxides such as potassium and sodium hydroxide are preferred. Such abase may be provided by adding alkali or alkaline earth metal oxide toan aqueous solution of the polyhydric alcohol composition or by theaddition to such an aqueous solution of a water-soluble alkali metalsalt whose aqueous solution is alkaline, as for example, sodiumcarbonate. However, the invention is not to be considered as limited tothe use of alkali or alkaline earth metal hydroxides as the bases ofother metals, ammonium hydroxide, or organic bases may be employed ifdesired.

In carrying out the alkaline degradationan aqueous solution of thereducing sugar containing polyhydric alcohol composition and the basicsubstance is heated to degrade the reducing sugar. While thetemperature'at which the alkaline degradation of the reducing sugar isconducted is The degradation is preferably conducted by heating thealkaline solution under atmospheric pressure at or about its boilingtemperature.

.. The exact nature of the degradation products of the reducing sugar isnot known, but these products are principally organic acids obtainedpresumably by rearrangement of the reducing ,sugar molecule due tointernal oxidation-reduction, as forex'ample, saccharinic acid, and byfragmentation or splitting of the reducing sugar 7 molecule and theformation of lower acids such .as pentonic, lactic, and'formic acids.presence of the'ba'sic substance these acids cons'u'rne a portion ofthe'alkali'ne material and appear in the form of their salts.

In the ,If desired, the'alkaline degradation of the re- 1 ducing sugarmaybe conducted in the'presence'of air or oxygen, but it has beenffoundthat the alkaline degradation can'be carried out in an inert atmospherewith almost equal ease and that the treatment in the presence of'airresults in a higher consumption of alkaline material per unit weight ofreducing sugar consumed.

Consequently, thealkaline degradation is preferably carried out in anatmosphere essentially free of oxqgen, as for example, by boiling thealkaline solution under a reflux condenser. The use of strong oxidizingagents in the alkaline degradation step tends to result in the oxidationof the polyhydric alcohol as well as the reducing sugar and hence isgenerally to be avoided.

The basic substance is'employed in a concentration such that atthe'b'eginning of the degra- ..dation, the" aqueous solution ofpolyhydric alcohol has a pH above 8.5. As the pH of the solution at thecommencement of the alkaline degradation is not critical as'long as thesolution has suflicient ialka'linity, the pH of the solution ispreferably adjusted to 10 or 1 1 to insure sufiicient alkalinity. Thedegradation products of the re ducing'sugar formed duringthe'alkalin'edegradation consume from 1 to about 4 equivalents of base per mol ofreducing sugar degraded to non-reducing compounds during the alkalinedegradation depending upon the composition and the conditions underwhich the alkaline degradation is conducted. Preferably, the basicsubstance is present in an excess of from about 5 to about 50% over theamount actually consumed by the alkaline degradation products of thesugar as such excess seems to cause a more complete degradation of thesugar. The excess of basic substance over the amount actually consumedby the alkaline degradation products remains in the solution uponcompletion of the degradation, and while proportions of base greaterthan an excess oi 50% over the amount actually consumed by thedegradation products do not interfere with the degradation, 'suc'hgreater proportions are not preferred because they result in anincreased load on the cation exchanger in the subsequent cation exchangestep.

Thus, where the alkaline degradation is conducted for one-half hourunder atmospheric pressure and at the boiling temperature of thesolution in the absence of substantial amounts of air, the basicmaterial will generally be consumedin a proportion of from about 1.6'to2.0 equivalents per mol of reducing sugar converted to nonreducingcompounds during the degradation. Assuming that the actual consumptionof basic substance during 'alkalinedeg'radation of a particularcomposition under these conditions is 1.6 equivalents per mol ofreducing sugar converted to non-reducing compounds, the alkalinedegradation will preferably beconducted with basic substance presentsomewhat in excess of this proportion, as for example, up to about 2.5equivalents per mol of reducing sugar so converted. If a deficiencybelow 1.6 equivalents of base per mol of converted reducing sugar beused under these conditions, essentially all of the basic material willbe combine'dwith degradation products and when an excess of basicmaterial is employed, a

'portionof the base remains at the conclusion of the alkaline"degradation.

If the alkaline degradation is conducted simila'rly except that oxygenbe'present (as by blowing with air) throughout the degradation, two ormore equivalents of base will generally be consumed per mol of reducingsugar converted to non-reducing compounds during the degradation and asin the case of the alkaline degradation in the absence of oxygen, it ispreferable to pro- 'vide"an excess of the basic material to assist in"portion of reducing sugar converted to non-reducing-compounds andtheamount of basic substance consumed underparticular degradationconditions can readily be determined 'by degradingasample'of thecomposition under such conditions'with basic substance present in'aproportion somewhat in excess of 4 equivalentsper mol of reducing'suga1' presentin' the original composition and'deterrnining''the'quantity of reducing compounds; and'basic substance remaining afterthe'deg'radation. Suchaproportion of basic sub stance based upon theoriginal sugar content will assure the presence of an excess of basebecause '4 equivalents of base per mol of reducing sugar .converted tonon-reducing substance is about the maximum that can be consumed. Inpracticing .the. preferred method, the proportion of basic substance maythen be adjusted to an amount somewhat in excess of that actuallyconsumed by the degradation products under the particular conditions.Such preferred amounts will generally fall within the range of from 1.05to 6.00 equivalents of basic substance per mol of reducing sugarconverted to non-reducing com- .pounds during the degradation.

It will be understood that the equivalents of base referred to areexclusive of base that may be utilized to neutralize other compoundsthat .may be present in the original polyhydric alcohol composition suchas metallic salts capable of forming metal hydroxides in the presence ofthe base, organic acid, or compounds which yield organic acid uponhydrolysis as, for example, lactones. However, such other compounds willbe removed from polyhydric alcohol compositions containing them whensuch compositions are treated in accordance with the process of thepresent invention.

Following the alkaline degradation, the composition is passed through acation exchange material capable of removing metal cations and replacingthem with hydrogen. In this manner the metal cations of the salts of theacids formed during the alkaline degradation and the metal cations ofany excess base remaining in the composition after the degradation arereplaced with hydrogen. As the cation exchanger material any of thecarbonaceous or resinous types which are capable of operating on thehydrogen cycle where X is the structure of the cation exchanger, M isthe cation and R is the anion, may be employed. As exemplary are thecarbonaceous cation exchange materials produced by the treatment oflignite or coal with sulfuric acid or equivalent, and the resinouscation exchange materials of the phenol-formaldehyde type. The cationexchanger materials sold under the trademark Zeokarb, Catex, andAmberlite IR-1 are exemplary of commercially available cation exchangematerials that are suitable for use.

When the eflluent from the cation exchanger fails to show the reductionin pH which normally "occurs in the passage of a salt-containingsolution therethrough the exchanger has become exhausted through thereplacement of all of the readily available hydrogen ions with metalions. The cation exchange material may thereupon be regenerated bypassing acid through the bed to radation of the reducing sugar and thecation exchange. In the case where the acid anion alone is adsorbed, theanion exchanger gives up a hydroxyl in exchange. Where the anionexchanger operates by adsorbing the whole acid molecule, it

.does not involve a true exchange, but the ac- ..tion is generallyreferred to an anion exchange and the term as used herein is intended toinclude regenerables of this type.

As the anion exchange material either the inorganic types such as thedolomite or heavy metal silicates or the organic types such as thosecontaining basic groups such as amine, quaternary ammonium or othernitrogen base groups may be employed. The resinous anion exchangers suchas the amine-formaldehyde resin exchangers are excellently suited foruse. Anion exchange materials sold under the trade-marks Anex, AmberliteIR-4 and Deacidite are exemplary of commercially available anionexchangers which may be employed.

When the eflluent from the anion exchanger fails to show the proper highpH value indicative of operation of the exchanger, the exchanger isapproaching exhaustion and may thereupon be regenerated by treatmentwith an alkali solution which either removes the acid moleculespreviously adsorbed or exchanges hydroxyl ions for acid anions dependingupon the way the anion exchanger operates.

The alkaline degradation is capable of converting most of the reducingsugar present in the original composition to non-reducing compoundswithout substantial effect upon the non-reducing polyhydric alcohol.Moreover, it has been found that a substantial proportion of thereducing compounds remaining after the alkaline degradation are usuallyconverted to a form such that they are removed by the subsequentcation-anion exchange treatment. As the cation-anion exchangers havesubstantially no effect upon the polyhydric alcohol present, it can beseen that the method utilizes alkaline degradation and cation-anionexchange for the ready and economical removal of reducing sugar frompolyhydric alcohol compositions without substantial conversion of thepolyhydric alcohol content to other chemical compounds.

I Non-limiting examples of the method of the present invention are asfollows:

Example I Sorbitol solution (28% H2O) grams 2,200 Water do 1,579One-half normal KOH cc This solution, which contained 60% water, wasboiled (104 C.) at atmospheric pressure in an atmosphere substantiallyfree of oxygen and with reflux of condensate for thirty minutes.

The reducing compounds present after the alkaline degradation amountedto 0.14% on a dry basis. In addition to the KOH required to neutralizethe free organic acid or lactones which were present in the originalsorbitol solution, the alkaline degradation consumed 0.56 gram of KOHper gram or about 1.8 mol of KOH per mol of sugar converted tonon-reducing compounds.

This alkaline treated solution having a pH of 10.25 was passed through acation exchange (Amberlite IR-l) column operating in the hydrogen cycle.The collected solution had a pH of 3.25. This solution was then passedthrough an anion evaporated to a water content of 26.3%.

tentwas -.044% as is.

exchange (Deacidite) column resulting in a'col- This solution was Ananalysis of the product, which had a very low lected solution of :pH6.55.

color value, showed .that reducing compounds present amounted toonly'.0'7% .(dr-y'basis) and that the sorbitol remained substantiallyunwhanged.

Example II Commercial sorbitolsolution prepared by the catalyticpressure hydrogenation of glucose and which had been filtered and freedof acids by passage through an anion exchanger was analyzedz-and'observedto contain 091% reducing sugar on 'a dry basis. Thissorbitol solution was used in making-the following composition:

Grams :Dilute sorbitol solution containing'83.9%

'waterand0.11% reducing sugar as is 12,214 43% NaOH .25

content of .023% as is or 0.12% dry basis.

Thealkali solution was then passed through a cation-exchange (Zeokarb)column operating in the hydrogen cycle and then'through an anionexchange '(Deacidite) column. After partial evaporation to 82.3% waterthe solution was 'found to contain {085% reducing sugar dry basis. Thesolution was further evaporated to approximately 50% solids, treatedwith three grams of sodium hydroxide pellets and the evaporationcontinued for two hours until the water content was 37.6%.

This solution which contained 038% reducing sugar dry basis was againpassed through a cation exchange (Zeokarb) column operating inthe-hydrogen cycle and through an anion exchange (Deacidite) column.After evaporation and treatment withactivated carbon .1918 grams of apractically water white solution was obtained which contained 30.9%water and .020% reducing sugar -dry' basis. 'The sorbitol inthis-solution was unaffected by the treatment.

Example III 30 cc. of one-half normal KOH were added to 1,000 grams ofglycerol solution containing 84.3% water, 0.63% of reducingsugar'believed to be glycerose, the per cent of reducing sugar beingreported as glucose, dry basis, and-a small proportion of impuritieshydrolyzable in the cold to acid. By per cent of reducing sugarreporte'd as glucose is meant that the reducing sugar, which wasbelieved to be glycerose, reduced Fehlings solution to the extent thatit would have been reduced by the stated percent of glucose. The alkalisolution was refluxed at about 100 C. for three hours, additionalone-half normal KO'H "being added in two 10 cc. increments during thelast two hours of refluxing. Of the KOH added approximately 32 cc. ofthe one-halfnormalsoluthe original composition in addition to removingreducing sugar. Thus, while as utilized in Examples I and II above themethod is supplemental to prior demineralization by filtering and cationexchange, the method is also excellently suited for the direct treatmentof undemineralized'sorbitol solution as it is received fromthe'hydrogenation equipment, the only difierence being that a somewhatlarger proportion of base .is consumed in the alkaline degradation stepdue to the alkali consumed in the formation of the hydroxides of themetals. Where the method of the present invention is applied toundemineralized solutions, it will remove the metal cations in thecation exchange step and any free acid, such as gluconic, will beremoved with the acidic degradation products of the reducing sugar inthe anion exchange step.

It is to be understood that the method of'the present invention may beutilized in conjunction with other treatments-if so desired. Forexample, a portion of the reducing sugar present may first be removed byfermentation and the method of the present invention utilized to removereducing sugar which remains after the fermentation treatment. Also,while the cation-anion exchange steps have been found to be quiteeffective in the removal of color bodies,it may be advantageous in thetreatment of certain polyhydric alcohol solutions to supplement themethod of the present invention with one or more activated carbontreatments. Such activated carbon treatments may be-given thecomposition prior to the alkaline degradation, between the cationexchange and anion exchange steps or after the anion exchange. Othersuch modifications of the method of the present invention will bereadily apparent to those skilled in the art.

Having described the invention what I .claim 1. The method of removingreducing sugar from an: aqueous polyhydric alcohol solution containingreducingsugar which comprises heating :un'der non'hydrogenatingconditions the said aqueous --solution-with a basic substance untilreducing sugar is degraded, passing the reacted mixture through a cationexchanger operating. in the hydrogen cycle and through an anionexchanger.

2. The method of removing reducing sugar from an aqueous polyhydricalcohol solutionxcontaining'reducing sugar which comprises heating undernon-hydrogenating conditions the said aqueous solution with a basicsubstance selected from the group consisting of alkali and alkalineearth metal hydroxides at a temperature above 60C. until reducing sugaris degraded, said basic substance being initially present in amount .of

from-5 to50% in excess of the amount of basic substance consumed duringdegradation, ssaid amount being within the range of from 1.05 to 6.00equivalents of base per mol of reducing sugar converted to non-reducingcompounds during the degradation and said amount being sufiicient toprovide an initial pH above 8.5, passing the reacted mixture through acation exchanger operating in the hydrogen cycle and through an anionexchanger.

3. The method of claim 1 and wherein the polyhydric alcohol is apolyhydric alcohol prepared by the reduction of reducible sugar.

4. The method of claim 2 and wherein the polyhydric alcohol is apolyhydric alcohol prepared by the reduction of reducible sugar.

JOHN D. BRANDNER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES The Amberlites, published by theResinous Products and Chemical Company, Philadelphia,

15 Pa., pages 1-12, third printing of Oct. 1942.

